The present investigation is intended to encompass the preliminary and developmental testing of a microprocessor controlled (SMART) stimulator. This device is intended to restore ability to stand and walk in paraplegics whose paralysis was the result of lesions of the spinal cord which have left the cell bodies of the alpha motor neuron pool innervating the legs intact. A variety of attempts have been made to use electrical stimulation to restore movement of the paralyzed. However, most types of electrical stimulation require large stimulation frequencies, factors which cause fatigue and damage to the muscles and result in poor control over movement. For this reason, in the present proposal, a method of sequential stimulation of the peripheral motor nerves is proposed. This technique offers the advantage of allowing smooth contractions in the range of normal physiological frequencies, good proportional control of movement, and low (typically 0.5 volts or less) stimulation voltages to tetanize the muscle. Movements such as walking, however, represent the complex interactions of a variety of muscles, contracting and relaxing at different times. Therefore, a microprocessor controlled stimulator is proposed which has feedback of the position and velociy of movement of the leg joints, and, from these data, appropriately controls the musculature to allow standing and walking. To avoid the complexities and risk of experimental procedures in humans, in these initial experiments, the hind leg of the cat will be used. The experiments will be conducted in 2 phases. First, the relationship of recruitment order, load, velocity of movement, and the fiber composition of the muscles will be assessed and a study of the movement of the hindlimb during walking will be made. From this data base, an empirical model of the hind limb of the cat will be derived to be used in the writing of a microprocessor program to operate a series of stimulators connected to the leg muscles. In the second phase spinal cord damage will be experimentally induced in the cats, and, following surgical implantation of the appropriate electrodes, an attempt will be made to restore standing and walking to these paralyzed animals. During this phase, an evaluation of long term effects of electrode implantation will be made.